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Endocrine Care: Michael B. Zimmermann, Hans Burgi, and Richard F. Hurrell Iron Deficiency Predicts Poor Maternal Thyroid Status during Pregnancy J Clin Endocrinol Metab 2007; 92: 3436-3440 [Abstract] [Full text] [PDF]

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mean corpuscular hemoglobin is the red blood cell index which might have been more indicative than m

Oscar M. Jolobe   (12 October 2007)

mean corpuscular hemoglobin is the red blood cell index which might have been more indicative than m 12 October 2007
Oscar M. Jolobe, retired geriatrician manchester medical society Send letter to journal: Re: mean corpuscular hemoglobin is the red blood cell index which might have been more indicative than m oscarjolobe{at}yahoo.co.uk Oscar M. Jolobe	I am writing to comment on the manuscript by Zimmerman et al. (1). In the model including body iron and week of gestation (but not transferrin receptor (TfR) or serum ferritin), the trend toward an association (P = 0.81) (1) might have been stronger had mean corpuscular hemoglobin (MCH) been the chosen red blood cell index in preference to mean corpuscular volume (MCV), given the fact that the former is a more sensitive indicator of iron deficiency (2, 3). Where iron deficiency was defined as a serum ferritin below 18 mcg/l, the superior sensitivity of subnormal MCH was exemplified by the fact that the proportion of iron deficient patients with MCH < 26 pg in the presence of MCV equal to or greater than 80 fl was significantly greater (P < 0.001) than the proportion of iron deficient patients with MCV < 80 fl in the presence of MCH equal to or greater than 26 pg, This reflects the fact that, despite nearly identical positive predictive values (58% vs 55%), MCH < 26 pg conferred a sensitivity of 97% for the diagnosis of iron deficiency as opposed to the sensitivity of 84.6% attributable to an MCV < 80 fl (2). Where iron deficiency was characterized by an increase in serum TfR levels, the superior sensitivity of subnormal MCH was exemplified by the fact that the inverse correlation was steeper between serum fR and MCH (r = -0.65, P = 0.0001) than between serum TfR and MCV (r = -0.47, P = 0.009) (3). The superior sensitivity of subnormal MCH is consistent with the fact that under-hemoglobinization of reticulocytes is an early manifestation of absolute iron deficiency (when the latter is defined as depletion of stainable bone marrow iron stores). This antedates the onset of significant microcytosis, more favorable diagnostic profile of the receiver operator characteristic (ROC) curve for reticulocyte hemoglobin content in comparison with the ROC curve for MCV (4). Under-hemoglobinization of components of the erythroid series is evident even at the preceding stage of iron deficient erythropoiesis, namely, functional iron deficiency, which can be induced by administration of recombinant erythropoietin to phlebotomized normal subjects. In the latter context under-hemoglobinization is exemplified by the production of hypochromic erythrocytes which are, nevertheless, of normal size (5). References 1. Zimmerman MB, Burgi H, Hurrell RF 2007 Iron deficiency predicts poor maternal thyroid status during pregnancy. J Clin Endocrinol Metab 92:3436-3440 2. Jolobe OMP 2000 Prevalence of hpochromia(without microcytosis) vs microcytosis (without hypochromia) in iron deficiency Clin Lab Haemotol 22:79-80 3. Kivivouri SM, Pelkomen P, Ylijoki H, Verronen P, Siimes MA 2000 Elevated serum transferrin receptor concentration in children with juvenile chronic arthritis as evidence of iron deficiency. Rheumatology 39:193-197 4. Mast AE, Blinder MA, Lu Q, Flax S, Dietzen DJ 2002 Clinical utility of the reticulocyte hemoglobin content in the diagnosis of iron deficiency. Blood 99:1489-1491 5. Brugnara C, Chambers L, Malynn E, Goldberg MA, Kruskall MS 1993 Red blood cell regeneration induced by subcutaneous recombinant erythropoietin: Iron deficient erythropoiesis in iron replete subjects. Blood 81:956-964